Verifying the identity of a person or group of people, referred to as authentication, has many uses in the context of computing. People often have multiple user accounts that employ some type of authentication before access to the account is granted. For example, a person may have accounts in the operating systems of their computing devices, accounts with social networking sites, accounts with online retailers, and so on. In many cases, the authentication is valid for a limited period of time, so that the user can continue to interact with the computer or network site during this period, but when the period expires, the user must be authenticated again.